The overall goals of the proposed studies are to establish the extent to which the receptive fields of individuals neurons in visual cortex are modifiable by short term (minutes to hours) manipulation of presynaptic and postsynaptic activity and their degree of correlation. The background for these studies is the long standing belief that this tissues is hard-wired and several recent demonstrations that synaptic weights, retinotopic maps, and even receptive field properties can be modified over short observation times. Our preliminary data support these demonstrations and suggest the need for systematic exploration of the modifiability of the dozen or so parameters which quantitatively describe these receptive fields and the distribution of this modifiability over cortical areas, layers, and cell types. In addition, we will use pharmacological techniques to ascertain whether the mechanisms supporting this plasticity are similar to those identified with the refinement of cortical function during postnatal development. Ultimately, this work will aid in the identification of general principles of plasticity applicable to all mammals throughout their lifetimes and to the identification of important differences between neocortex and other parts of the brain insofar as the detailed mechanisms of plasticity are concerned.